API Design Guide Version 1.0

This PR proposes an API design guide for use at Wikia. It is opinionated about the use of standards for error handling, media types, and HTTP protocol usage. The state of the art in the industry for building APIs has progressed to the point where developers can focus less on attribute naming and protocol semantics and more on solving application specifics. 

With standards like [HAL](http://stateless.co/hal_specification.html) and [JSON-LD+Hydra](http://www.hydra-cg.com/) (among others) all [three layers of API semantics](http://amundsen.com/blog/archives/1138) are closer to being standardized. This means that as a developer you need not spend a lot of time noodling over the JSON payload layout, client-server interactions or API libraries. Use one of the standards mentioned [above](https://github.com/mikekelly/hal_specification/wiki/Libraries) and the above comes (mostly) included.

That said, I'm sure it's also not perfect. It has not (all) been refined by the fire application. It's a work in progress. If you have suggestions or improvements, please open a PR! We also have a [slack channel](https://wikia.slack.com/archives/api-design) for API design. Come and ask questions [there](https://wikia.slack.com/archives/api-design). Feedback is welcome and encouraged.
I would suggest only HAL or only JSON-LD. If a special use case arises, then it should be discussed as an exception but we should not begin by allowing exceptions.